Soundboards for string instruments having plastic foam body with harder outer layers

ABSTRACT

A soundboard is made of a body of plastic foam material which is supplemented by means for improving the vibration transmission characteristics. The means may be a pair of cross-grained thin sheets of harder material than the plastic foam material bonded on both surfaces of the body or may be inserts of harder material disposed in through-holes perforated in the soundboard, the inserts abutting directly on a bridge and ribs, respectively, coupled to both surfaces of the soundboard.

Umted States Patent 1191 1 3,724,312 Yamada et al. 1451 A r. 3 1973 [54]SOUNDBOARDS FOR STRING [56] References Cited INSTRUMENTS HAVING PLASTICFOAM BODY WITH HARDER OUTER UN'TED STATES PATENTS LAYERS 3,477,33011/1969 [75] Inventors: Takashi Yamada, l-lamamatsu;

'goylilisafkir Matsumoto, Toyohashi, 1:370:l71 8/1932 0t 0 apan 73Assignee: Nippon Gakki Seizo Kabushiki Primary Examiner-Richard Wfl qKaisha Shizuokwken, Japan Assistant Examiner-Lawrence R. Franklm [22]Filed Mar 23 1971 Attorney-Flynn& Frishauf o 211 Appl. 1 10.; 127,183ABSTRACT A soundboard is made of a body of plastic foam [30] ForeignApplication priority Data material which is supplemented by means forimproving the vibration transmission characteristics. The Mar. 26, 1970Japan ..45I25052 means may be a pair of crossgrained thin sheets of 1970Japan AS/25053 harder material than the plastic foam material bondedApr. 10,1970 Japan ..45/30 on both surfaces of the body or may beinserts of Mar. 26, 1970 Japan ..45/28389 harder material disposed inthroughmoles perforated in the soundboard, the inserts abutting directlyon a ill "84/123349 bridge d ribs, respectively, coupled to bothsurfaces C fth db [58] Field of Search ..84/192-196 o 8 oar 15 Claims,11 Drawing Figures PATENTEDAPR 3 ma SHEET 1 0F 2 FIG.2

FIG. 1

FIG.3

FIG.5

PATEMEDAPR 3 m5 3, 724, 3 1 2 SHEET 2 [1F 2 SOUNDBOARDS FOR STRINGINSTRUMENTS HAVING PLASTIC FOAM BODY WITH HARDER OUTER LAYERS Thisinvention relates to soundboards for string musical instruments and moreparticularly to those adapted for use in a piano.

A string musical instrument, for example, a piano is provided with asoundboard to transmit the vibrations of the strings to the air so thatan increased sound output is obtained. The conventional soundboard hasgenerally been made of spruce wood. Since the spruce which is of naturalgrowth does not have uniform quality, it presents difficulties inproviding soundboards having uniform performance. Further, a woodensoundboard expands or contracts according to variations in ambienttemperature or humidity, with the resulting change in the quality ofmusical tones transmitted therethrough. The too small internal loss ofthe spruce also leads to prominent variations in the volume of highpitch tones when they are transmitted through a soundboard prepared fromthe wood. Further, the characteristic quality of the spruce limits theratio of Youngs modulus to a density which is desired to be sufficientlylarge to obtain good responses with respect to high pitch tones. Sincethe spruce soundboard naturally has grains which cause the vibrations ofthe strings to be transmitted predominantly in the direction of thegrains, it is necessary for elimination of this drawback to mount ribson the soundboard at right angles to the direction in which the grainsare formed.

To avoid the aforementioned disadvantage of a wooden soundboard, therehas been proposed in recent years the application of a different type ofsoundboard prepared from a foamed plastic material. Such soundboard islittle affected by ambient temperature and humidity and permits easymanufacture. However, this type of soundboard has shortcomings. That is,the foamed resin material has not only elasticity but relatively largeviscosity as well, and the vibration energy applied thereto quicklydisappears and fails to be transmitted to the surrounding area. In otherwords, the frequency characteristics of the aforesaid soundboarddecrease as the sounds to be generated have higher frequency.

The object of this invention is to provide a soundboard which is littleaffected by ambient temperature and humidity, presents proper internalloss, permits easy manufacture and has good vibration transmissioncharacteristics.

SUMMARY OF THE INVENTION According to an aspect of this invention, thereis provided a soundboard for use in a string musical instrument whichcomprises a body of plastic foam material, and means for improving thevibration transmission characteristics, the means comprising first andsecond reinforcement members made of harder material than the plasticfoam material bonded to the major surfaces of the plastic foammaterialthe grains or fibers of the reinforcement members crossing eachother substantially at right angles to each other.

As used herein and in the claims appended hereto, the term fibersdenotes not only unidirectionally fibers in a plastic-type material, butalso the grain of a wooden material.

This invention can be more fully understood from the following detaileddescription when taken in connection with the accompanying drawings, inwhich:

FIG. 1 is a longitudinal sectional view of an upright piano;

FIG. 2 is a sectional view of a soundboard according to an embodiment ofthis invention for use in a piano;

FIG. 3 is a sectional view of a soundboard according to anotherembodiment of the invention;

FIG. 4 is an exploded perspective view of the soundboard of FIG. 3;

FIG. 5 is an exploded perspective view of a modification of thesoundboard of FIG. 3;

FIG. 6 is an exploded perspective view of anothe modification of thesoundboard of FIG. 3;

FIG. 7 shows an elevation of a soundboard according to anotherembodiment of the invention;

FIG. 8 is a sectional view on line VIII-VIII of FIG.

FIG. 9 is a sectional view on line IX-IX of FIG. 8;

FIG. 10 is an elevation of a soundboard according to still anotherembodiment of the invention; and

FIG. 11 is a sectional view on line Xl-XI of FIG. 10.

There will now be described by reference to FIG. 1 the construction of apiano in which there is applied the soundboard of this invention.Stretched across a piano frame 2 is a plurality of strings I fastened totuning pins 3 and hitch pins 4. When the string 1 is struck with ahammer 5 to generate tones, the vibrations of the string 1 aretransmitted to a soundboard 6 through a bridge 7 mounted thereon againstwhich there is pressed the string 1, so as to produce tones in amplifiedform. The peripheral edge of the soundboard 6 is fixed to a supportingframe 8. While FIG. 1 represents an upright piano, a grand piano has asimilar construction.

FIG. 2 illustrates a soundboard according to an embodiment of thisinvention. According to this embodiment, the soundboard 6 is prepared bysandwiching a low density core 11 made of a plastic foam material suchas a foamed form of acryl, styrol or urethane between first and secondthin reinforcement members 12 and 13 consisting of glassfiber reinforcedplastic harder than the plastic foam material. The core 11 has athickness of 8 to 13 mm and a specific gravity of 0.05

to 0.3, preferably 0.1. The reinforcement members 12 and 13 are formedof a glass mat or cloth whose fibers intersect each other substantiallyat right angles or another type of glass cloth prepared by laminatingtwo sheets each having a roving stretched only in one direction in sucha manner as to cause the rovings to intersect each other at rightangles.

The plastic materials reinforced by the glassfiber to form theaforementioned glassfiber reinforced plastics may consist of polyesteror epoxy resin. The reinforcement member 12 or 13 preferably has athickness of 0.5

to 1.0 mm. Since these members 12 and 13 can be formed into pre-pregsheets and thermally set at a temperature of about l00C on the surfaceof the core 11, there is no need to use any extra adhesive to bondthecore 11 and reinforcement members 12 and 13 together. Thereinforcement members 12 and 13 thus formed act as means for improvingthe vibration transmission characteristics of the core 11. Further, thesoundboard 6 as a whole should preferably have a specific gravity ofabout 0.3 to 0.5.

With the soundboard according to the embodiment of FIG. 2, there is usedsynthetic resin in the core 11 and reinforcement members 12 and 13 torealize a large ratio (about 32.4 X of Youngs modulus to density. Thethickness of the core 11 may be varied to cause a soundboard to have anoptimum stiffness and weight. The glass-fiber reinforced plastic memberswhose internal loss is appreciably larger than in a spruce soundboardgives good results as the sound propagating member of a string musicalinstrument. The reinforcement member made of resin-impregnated glass maybe formed to a thickness of 0.5 to 1 mm so as to obtain great stiffness.This helps tones ranging from a low to a high pitch to be transmitted ingood condition. Since the glasstibers constituting the reinforcementmember intersect each other at right angles, there is no need to useribs. The soundboard of FIG. 2 entirely formed of synthetic resin islittle affected, as is naturally expected, by ambient temperature andhumidity.

FIGS. 3 to 6 illustrate a soundboard according to another embodiment ofthis invention. The core 21 is prepared, as in the embodiment of FIG. 2,from a foamed form of acryl, styrol or urethane with a thickness of 8 to13 mm. In the case of FIGS. 3 to 6, there are bonded to both sides ofthe core 21 reinforcement members each 0.5 to 1.0 mm thick made ofwooden material such as lauan or birch. Reinforcement members 22 and 23or 24 and 25 are so laminated on each side of the soundboard as to causethe grains extending in the direction of the arrows of FIG. 4 tointersect each other at right angles.

With the laminated soundboard of FIGS. 3 and 4, the grains oftworeinforcement members laminated on either side of the core 21 intersecteach other at right angles, so that the magnitudes of flexural rigidityin the directions of the respective grains can be balanced, eliminatingthe necessity of additionally using ribs as is the case with theconventional soundboard. This has the further advantage that a resonanceof 1,000 to 3,000Hz which would otherwise be generated between theadjacent ribs is removed and the soundboard is lightened by the weightof the ribs, thereby increasing the sound transmission efficiency.

The wooden reinforcement member has a relatively large flexuralrigidity, enabling elastic waves derived from the vibration energyapplied thereto to be transmitted through the entire soundboard in goodcondition, and displaying a full sound-propagating characteristic withrespect to tones ranging from a low to a high pitch.

Where the outermost wooden reinforcement members 23 and 25 are sodisposed as to cause the directions of the grains to intersect eachother at right angles as shown in FIG. 4, the soundboard can be made,after bonding, to warp for better propagation of sounds, utilizing thefact that the soundboard expands or contracts according to ambienttemperature to different degrees between the grain direction and anotherdirection perpendicular thereto. An adhesive for the reinforcementmember preferably consists of watersoluble vinyl acetate systems orglue.

FIGS. 5 and 6 illustrate modifications of FIGS. 3 and 4 respectively.With the soundboard of FIG. 5, there are mounted on both sides of thecore 21 wooden reinforcement members 22 and 24 respectively so as tocause the directions of grains to intersect each other at right angles.7

With the soundboard of FIG. 6, there are laminated on each side of thecore 21 three wooden reinforcement members as 22 23 26 and 24 25 27 insuch a manner that the grain directions of the adjacent reinforcementmembers intersect each other at right angles.

FIGS. 7 to 9 illustrate a soundboard according to another embodiment ofthe invention. According to this embodiment, the soundboard of a plasticfoam material'is not supplemented by reinforcement plate members as inthe above embodiments. The soundboard is reinforced only by a number ofconventional rib members.

However, it has been found that if a soundboard body of plastic foammaterial is supplemented only by a number of spaced rib members attachedto one side of the soundboard body, such soundboard shows a very poorvibration propagation characteristic. On such soundboard, a bridge isconnected to the rib members with the soundboard body of plastic foammaterial interposed therebetween. This body of plastic foam materialnaturally has a low stiffness in the direction of its thickness and isliable to be compressed easily, having a tendency not to be vibratedsufficiently in full conformity with the vibration of the bridge.Therefore, the vibration transmitted to the bridge from the strings ismostly damped by the soundboard body, failing to be transmitted furtherto the rib members with most of the vibration energy lost at thatsoundboard body. This loss of vibration energy becomes high, especiallyat the treble or high frequency tone region. Namely, the higher thefrequency at which the bridge vibrates, the more prominent the lossbecomes. Accordingly, particular consideration should be given to thecase wherein the soundboard body of plasticv foam material is providedwith rib members, in order to assure effective transmission of thevibration of the bridge to the rib members.

FIGS. 7 to 9 illustrate an improved device or means for improving thevibration transmission characteristics of such soundboard. ThroughoutFIGS. 7-9, numeral 31 generally represents a soundboard of a plasticfoam material of any of the forms shown in FIGS. 1-11. On the undersideof the soundboard 31 are arranged side by side a plurality of ribs 32 ina diagonal direction, the ribs being fixedly attached to thesoundboard.On the upper surface of the soundboard is mounted a bridge 33intersecting the ribs 32 at an angle thereto. Those parts of thesound-board 31 which are disposed between the plural ribs 32 and bridge33 are perforated with through holes 37. Into the through holes 37 areinserted ring-shaped members 34 made of harder material than the plasticfoam material and having an excellent capacity of transmittingvibrations. The members 34 may consist of metal such as aluminum orwooden materials such as maple, beech, or box-wood or thermosettingresins of little shrinkage such as epoxy or polyester. The ring-shapedmembers 34 are formed with an equal thickness to that of the soundboard31 and are so disposed in the holes 37 as to abut on the bridge 33 andribs 32.

According to the aforementioned embodiment, the bridge 33 and ribs 32are joined together by means of the ring-shaped members or inserts 34.Since the members 34 are made of a material having a good vibrationtransmitting capacity, that is, a large compression strength, vibrationsof the bridge 33 resulting from those of the string are transmitted tothe ribs without being attenuated by the foamed resin materialconstituting the soundboard, enabling high frequency tones as well asthe high harmonics associated with bass, medium and treble tones to befully generated. Referring to FIG. 9, numeral 35 denotes a string and 36a string holding member.

The soundboard of the aforementioned various constructions is fixed to asupport frame on the peripheral edge, increasing the flexural rigidityof the peripheral portion and in consequence unavoidably deterioratingthe vibration characteristics of the soundboard.

Therefore, with a soundboard whose core consists of foamed resinmaterial, it may be contemplated to reduce the peripheral thickness ofthe core for improvement of the vibration characteristics of thesoundboard. Such method, however, presents practical difficulties.Alternatively, it may be considered to form notches or many holes alongthe peripheral edge of the soundboard in order to decrease the stiffnessof the peripheral portion. With the soundboard of this invention,however, which comprises a core and reinforcement members laminatedthereon, as in FIGS. 3 to 6, using an adhesive agent of syntheticorganic material, the adhesive agent coated on the inner wall of theaforementioned notches or holes is deteriorated in quality during longexposure to the atmosphere, resulting in a prominent decrease in themechanical strength of the core and the bonding force of the adhesiveagent.

In view of the aforementioned drawbacks, there is provided, asillustrated in FIGS. and 11, a soundboard which is improved in thevibration characteristics by reducing the stiffness of its peripheralportion. As in the above-mentioned embodiments, there is laminated oneach side of a foamed resin core 41 of 8 to 11 mm thickness groupsconsisting of a plurality of (for example, two) reinforcement members as42 43 and 44 45, respectively, made of aluminum, glassfiber reinforcedplastic, or wood. If there is used an aluminum sheet, it is onlyrequired to be 0.3 to 0.5 mm thick. The inner reinforcement members 42and 44 brought into direct contact with the core 41 have an equal areathereto so as fully to face it. The other outer reinforcement members 43and 45 have a smaller area than the inner reinforcement members 42 and44. Member 43 has an irregular shape as shown by its outline 51 in FIG.10. As indicated in FIG. 11, only part of the periphery of the outerreinforcement member 43 contacts the inner reinforcement member 42. Onthe outer reinforcement member 43 is disposed a bridge 46. The innerreinforcement member 44 is fixed on the peripheral edge to a frame 47.

A soundboard of the aforementioned construction is formed thinner on theperiphery than at the central part so as to be reduced in stiffness atthe periphery and in consequence exhibit improved vibrationcharacteristics.

What we claim is:

1. A soundboard for use in a string musical instrument comprising: abody of plastic foam material; a bridge attached on one surface of saidbody; rib members attached on the other surface of said body andcrossing said bridge at angles thereto; said body having through-holesperforated between said bridge and said rib members; and a plurality ofinserts of harder material than said plastic foam material, said insertsbeing disposed in said through-holes and abutting on said bridge and ribmembers.

2. A soundboard for use in a string musical instrument comprising:

a body of plastic foam material, said body having generally opposingmajor surfaces; and first and second reinforcement members bondedrespectively on both major surfaces of said body, said reinforcementmembers having substantially unidirectionally running fibers, the fibersof said reinforcement members crossing substantially at right angles toone another, and said reinforcement members being formed of hardermaterial than said body.

3. A soundboard as claimed in claim 2 wherein the fibers of said firstreinforcement member run substantially in one direction, and the fibersof said second reinforcement member run in a direction substantiallyperpendicular to said one direction.

4. A soundboard as claimed in claim 2 wherein each of said first andsecond reinforcement members comprises a plurality of layers bondedtogether, the fibers of adjacent ones of said layers crossingsubstantially at right angles to each other.

5. A soundboard as claimed in claim 2 further comprising third andfourth reinforcement members bonded respectively on said first andsecond reinforcement members, said third and fourth reinforcementmembers being formed of harder material than said body, said third andfourth reinforcement members being smaller in area than said first andsecond reinforcement members.

6. A soundboard as claimed in claim 5 wherein said third and fourthreinforcement members are disposed substantially on the central part ofsaid soundboard body.

7. A soundboard as claimed in claim 5 further comprising: a bridgeattached on the outer surface of said third reinforcement member; ribmembers attached on the outer surface of said fourth reinforcementmember, said rib members crossing said bridge at angles thereto; and aplurality of inserts of harder material than said plastic foam material,said inserts being disposed in through-holes perforated in saidsoundboard body and abutting on said bridge and rib members.

8; A soundboard as claimed in claim 5 wherein said third and fourthreinforcement members have a higher Youngs Modulus than that of saidbody.

9. A soundboard as claimed in 2 further comprising a bridge attached onthe outer surface of said first reinforcement member; rib membersattached on the outer surface of said second reinforcement member, saidrib members crossing said bridge at angles thereto; and an insert ofharder material than said plastic foam material, said insert beingdisposed in a through-hole perforated in said soundboard body andabutting on said bridge and rib members.

10. A soundboard as claimed in claim 9 comprising a plurality of saidinserts disposed in respective throughholes perforated in saidsoundboard body, said inserts abutting on said bridge and rib members.

11. A soundboard as claimed in claim 2 wherein said reinforcementmembers are substantially thinner than said body of plastic foammaterial.

12. A soundboard as claimed in claim 2 wherein said reinforcementmembers comprise members formed of hard wood.

13. A soundboard as claimed in claim 2 wherein said reinforcementmembers comprise members formed of plastic material reinforced withunidirectionally

1. A soundboard for use in a string musical instrument comprising: abody of plastic foam material; a bridge attached on one surface of saidbody; rib members attached on the other surface of said body andcrossing said bridge at angles thereto; said body having through-holesperforated between said bridge and said rib members; and a plurality ofinserts of harder material than said plastic foam material, said insertsbeing disposed in said through-holes and abutting on said bridge and ribmembers.
 2. A soundboard for use in a string musical instrumentcomprising: a body of plastic foam material, said body having generallyopposing major surfaces; and first and second reinforcement membersbonded respectively on both major surfaces of said body, saidreinforcement members having substantially unidirectionally runningfibers, the fibers of said reinforcement members crossing substantiallyat right angles to one another, and said reinforcement members beingformed of harder material than said body.
 3. A soundboard as claimed inclaim 2 wherein the fibers of said first reinforcement member runsubstantially in one direction, and the fibers of said secondreinforcement member run in a direction substantially perpendicular tosaid one direction.
 4. A soundboard as claimed in claim 2 wherein eachof said first and second reinforcement members comprises a plurality oflayers bonded together, the fibers of adjacent ones of said layerscrossing substantially at right angles to each other.
 5. A soundboard asclaimed in claim 2 further comprising third and fourth reinforcementmembers bonded respectively on said first and second reinforcementmembers, said third and fourth reinforcement members being formed ofharder material than said body, said third and fourth reinforcementmembers being smaller in area than said first and second reinforcementmembers.
 6. A soundboard as claimed in claim 5 wherein said third andfourth reinforcement members are disposed substantially on the centralpart of said soundboard body.
 7. A soundboard as claimed in claim 5further comprising: a bridge attached on the outer surface of said thirdreinforcement member; rib members attached on the outer surface of saidfourth reinforcement member, said rib members crossing said bridge atangles thereto; and a plurality of inserts of harder material than saidplastic foam material, said inserts being disposed in througH-holesperforated in said soundboard body and abutting on said bridge and ribmembers.
 8. A soundboard as claimed in claim 5 wherein said third andfourth reinforcement members have a higher Young''s Modulus than that ofsaid body.
 9. A soundboard as claimed in 2 further comprising a bridgeattached on the outer surface of said first reinforcement member; ribmembers attached on the outer surface of said second reinforcementmember, said rib members crossing said bridge at angles thereto; and aninsert of harder material than said plastic foam material, said insertbeing disposed in a through-hole perforated in said soundboard body andabutting on said bridge and rib members.
 10. A soundboard as claimed inclaim 9 comprising a plurality of said inserts disposed in respectivethrough-holes perforated in said soundboard body, said inserts abuttingon said bridge and rib members.
 11. A soundboard as claimed in claim 2wherein said reinforcement members are substantially thinner than saidbody of plastic foam material.
 12. A soundboard as claimed in claim 2wherein said reinforcement members comprise members formed of hard wood.13. A soundboard as claimed in claim 2 wherein said reinforcementmembers comprise members formed of plastic material reinforced withunidirectionally running glass fibers.
 14. A soundboard as claimed inclaim 2 wherein said reinforcement members have a higher Young''sModulus than that of said body.
 15. A soundboard as claimed in claim 2wherein said reinforcement members comprise members formed of woodenmaterial, said unidirectionally running fibers comprising the grain ofsaid wooden material.